In U.S. Pat. No. 5,778,083 issued 7 Jul. 1998 to Godfrey is disclosed a surround sound microphone known under the trade mark “Holophone”. This was first marketed in 1999 and company literature states that the Holophone “covers virtually all forms of microphone technology for recording in surround sound, including the number of channels or kind of pick-ups for a wide variety of applications”. The Holophone is extremely expensive and complex as a design for recording surround sound, the device is not currently being sold. The patent discloses a microphone system includes a portable frame for mounting linear pick-up microphones such that each of the microphones has its diaphragm facing outwards from the frame and the diaphragms form a generally elliptical pattern. A microphone with a substantially hemispherical pick-up pattern is mounted on the frame such that it is directed upwards and a second substantially hemispherical pick-up pattern microphone is mounted on the frame directed downwards. The linear pick-up pattern microphones are equi-spaced about the perimeter of the frame. There is a hand or camera grip depending downwards from the frame. The microphones of the frame can be electronically connected to the respective channels of a multi-channel sound system, or to the channels of a digital mixer which in turn can be connected to a multi-channel sound recording device. The microphones may be selectively electronically connected to adapt the system for a predetermined sound playback configuration.
The patent claims that in all cases the object must be an elliptical, non-circular pattern or “shape” critical to the microphone placement; the preferred embodiment of the mounting frame or object itself is described as “generally football-shaped”.
The patent does not describe the shape of the associated ellipse (the frame) upon which the microphones are mounted as being integral to effecting the reception of sound by the object.
Further, the patent specifies that the lateral microphones must be spaced equidistant from one another, with a control of the pick-up pattern (number of channels and/or type of surround recording) switched electronically, remote from the device. The patent specifies hypercardiod microphones in fixed placement around the elliptical shape, with no numerical specification made to the amount of microphones.
While the end-user could switch electronically between microphones much as is specified in the patent, this ability to do so is not specific to the Modular Microphone Array design.
In U.S. Pat. No. 4,042,779 (Craven and Gerzon) issued August 1977 is disclosed a device, based on a set of principles for recording a multi-channel, surround soundfield in a manner termed B Format. The principles behind the Soundfield are not directly compatible with the type of recording currently necessary for the ITU R 775BS specification for the playback of 5.1 channel surround sound, though work is progressing on digital signal processing (DSP) algorithms that transform B Format recordings into the ITU R 775BS playback standard.
In professional literature (G. Theile, Das Kugelflachenmikrofon, 14 Tonnemeistertagung des VDT, Pp 277-293, 1986). Is disclosed the Schoeps Sphere stereo Microphone KFM 6 which was designed by Dr. Gunther Theile for German microphone manufacturer Schoeps GmbH. The Stereo Sphere is based on the use of a 200 mm wooden ball-shaped sphere, in which are mounted two opposing transducers.
A further version of this design, the Schoeps KFM 360, derives multichannel surround sound through the addition of two figure-of-eight transducers, externally mounted in relation to the existing two opposing transducers. The developer of this version of the Schoeps Sphere, Jerry Bruck (New York City), has stated in print that this design is unpatented and “dedicated to the public domain” for further development. This is a design that differs from the arrangement disclosed herein in four key areas. First, the shape is fixed as a sphere. Second, in addition to the two transducers as found in the original KFM 6 design, that are of fixed location within the sphere, the KFM 360 has the two additional figure-of-eight transducers placed externally, adjacent to the two internally mounted transducers and the surface of the sphere. Third, the object described depends on signal processing to be effective. Fourth, the device is limited to recording only to four channels.
In U.S. Pat. No. 4,658,932, April 1987 (Michael Billingsley) and U.S. Pat. No. 4,361,736 (Ronald Wickersham and Edward Long) is disclosed a device manufactured as the Crown PZM and SASS microphone systems which makes use of the pressure zone effect, which combines the direct sound with the first reflection from a nearby boundary to produce a coherent pickup by the microphone transducer.
In the pressure-zone approach, the linear bandwidth of the transducer is (in part) dependent upon the spacing of the transducer from the reflecting surface. This PZM approach trades off the out-of-band cancellation effects for the in-band additive effects that result from summation of direct and reflected sound reaching the transducer diaphragm. The mounting configurations for the transducers used in our device do not use the pressure zone effect. Instead, the transducers are mounted in a coplanar manner that avoids the cancellation effects of nearby surface reflections across the entire frequency-range of the transducer.
In European patent EP 0 848 572 A1 (Hitoshi Ishiwata) is disclosed a microphone unit comprising a semi-spherical structure base, a first microphone element having at least two directivities which is attached to a left end of the structure and a second microphone element having at least two directivities which is attached to a right end of the structure. The patent describes a semi spherical shape, ranging from 10 to 50 cm in diameter, with four directional microphones mounted in pairs, back-to-back on opposing sides of the sphere's surface. This arrangement results in two microphones facing forwards and two facing rearwards on the lateral plane. The resultant sound pick-up provides either a two or four channel output, dependant on the routing and processing of the signals received from the two or four microphones. The patent further describes processing of the output signal as integral to providing the desired results of a stereo (2 channel) or “natural sound” (4 channel) output from the device.
The patent describes a design that differs from the arrangement disclosed herein in three key areas. First, the shape is fixed as a sphere. Second, the transducers are fixed in one location on top of the surface of the sphere. Third, the object described depends on signal processing to be effective.
In U.S. Pat. No. 6,041,127 (Elko) issued March 2000 and assigned to Lucent Technologies is disclosed a first-order differential microphone array with a fully steerable and variable response pattern. One illustrative embodiment of the present invention comprises a microphone array consisting of 6 small pressure-sensitive omni-directional microphones flush-mounted on the surface of a ¾″ diameter rigid nylon sphere. The microphones are advantageously located on the surface at points where included octahedron vertices contact the spherical surface. By selectively combining the three Cartesian orthogonal airs with scalar weightings, a general first-order differential microphone beam (or a plurality of beams) is realized which can be directed to any angle (or angles) in three-dimensional space. The microphone array may find use in surround sound recording/playback applications and in virtual reality audio applications.
Calling on an elaborate digital signal processing of the output signals of its sphere-mounted microphones, the Steerable and Variable First-order Differential Microphone Array is attempting to create a first-order, directional microphone with a steerable signal. The small sphere has six omni-directional transducers (in the illustrated design) mounted in an orthogonal relationship on the surface of the ¾″ diameter sphere, such that with the application of digital signal processing to any variety of signal combinations, various directional patterns of audio reception can be derived from the output.
The patent claims that the device can be used for surround sound applications in the abstract of the invention, but this is not elaborated further in the body or claims sections of the patent. The output of a surround sound signal from this device would most likely exhibit some of the qualities as found in a B Format signal (see above, Soundfield/Gerzon) and present DSP challenges in deriving a standard ITU R 775BS, 5.1 channel surround sound output, due to the microphone positions and spacing obtained from the ¾″ sphere. This is a design dependant on specialized processing to derive a surround output;
U.S. Pat. No. 4,675,906 (Sessler and West) issued June 1987 discloses a thin-walled, plexiglas cylinder of 5 cm outer diameter, hollow with two open ends serves as the mounting device for four bi-directional microphones, at 90 degree intervals on the wall of the cylinder, as seen from above. The microphones are mounted “symmetrically” to the cylinder: flush, with one lobe of the bi-directional element of each microphone facing outwards and the second lobe facing inwards. The open nature of the cylinder thus allows the reception of sound waves traversing the cylinder to be received at different intensities; the combination of the inner and outer facing lobes of each microphone creates a distinct directional reception of sound. Combined, the four microphones have a toroidal pick-up pattern about the cylinder, with a distinct bias towards frequency reception in the range of human speech. Thus, the device is designed as a single output (monaural) microphone array for use in applications such as conferencing.
Two further systems have recently been developed in Germany. The systems are both open framework mounting structures, relying on a suspension system composed of a central mounting hub and connected metal tubing that allows microphones to be suspended in space. The first system has fixed extensions from the centre; the second—currently in prototype form—accommodates adjustment. The systems are:
The SPL/Brauner Atmos 5.1 which has five booms extending from a centre point, each fixed in distance from that point. Specific Brauner brand microphones, with pressure gradient transducers facing outwards from center, are mounted on the ends of the booms. The five microphones do not make use of physical boundaries or structures beyond the typical transducer diaphragm and housing. This configuration came on the market in 1999 and is still available.
The Optimized Cardiod Triangle—OCT, which is another design by Gunther Theile (see Schoeps Sphere), the OCT has adjustable tubing that can alter, within small increments of up to approx 20 cm, the spacing of an array of individual microphones. As with the SPL/Brauner device, this design does not make use of physical boundaries or structures between all microphones beyond the typical transducer diaphragms and housings.